Sensor network technology in which numerous sensors are installed in an installation area, detection information obtained by the respective sensors is wirelessly transmitted, and the detection information is collected by a base device that can wirelessly communicate with a sensor in the installation area is conceivable. In such a sensor network, for example, it is further conceivable that it is desirable to monitor temporal changes of the detection information of each sensor. In this case, identification information is set for each sensor and correlated management of the identification information and detection information is necessary.
To set identification information for a sensor, it is conceivable that at the time of manufacture or setting of the sensor, a writing tool such as a read-only memory (ROM) writer is used to set individually unique identification information in a non-volatile area of the ROM in the sensor. However, in cases where there are an extremely large number of sensors, problems arise including the huge amount of work required for such setting, and increased manufacturing and installation costs.
Further, to detect the position of multiple sensors, there is a technique of disposing two sensors to which identification information is respectively given and whose positions are known; and from the communication time that these two sensors to communicate with another sensor, a distance is obtained whereby, the position of each sensor is obtained (for example, refer to Japanese Laid-Open Patent Publication No. 2009-250627). According to another technique, to prevent unauthorized copying of a multilayer optical recording medium, identification information based on the distance between base points of the recording layers is used to identify the multilayer optical recording medium (for example, refer to Japanese Laid-Open Patent Publication No. 2003-242653).
A case is conceivable where a large number, e.g., several hundred to several tens of thousands, of low-cost chip sensors are arranged as a sensor network. In this case, that which improves the function of the sensors and the technical direction differ. The number of sensors is set to a relatively large number according to the degree to which the function of the sensors is curbed and as a result, the volume of detection information that can be detected by the sensor network overall increases.
In this type of simple sensor network that uses a large number of simple-function sensors, the ability to continuously monitor temporal changes of the detection information for each of the sensors, which are of a large number, becomes more important than accurately grasping the positions of the sensors. Additionally, a way to simply set, by using a simple configuration, the identification information of the large number of sensors dispersed throughout the installation area is desirable.